The long term goal of this project is to characterize the structure and function of P-57, a novel calmodulin (CaM) binding protein from brain. We have recently purified P-57 to apparent homogeneity from bovine cerebral cortex membranes. In contrast to other CaM binding proteins, P-57 apparently has higher affinity for CaM in the absence of bound Ca2+ than in its presence and Ca2+ causes the release of CaM from P-57. It is hypothesized that P-57 may function to bind CaM at some local site within the cell and release CaM in response to increases in free Ca2+. The specific aims of this project include quantitation of binding between P-57 and CaM in the presence and absence of Ca2+, determining if P-57 interacts with other polypeptides in brain, examination of the tissue distribution of P-57, characterization of the physical properties of P-57, characterization of cAMP dependent protein kinase catalyzed phosphorylation of P-57, and determination of the influence of phosphorylation on the affinity of P-57 for CaM. Homogeneous P-57 in mg quantities, anti-P57 rabbit polyclonal antibodies, and fluorescent labeled CaM derivatives are currently available for the proposed experiments.